did you leave a small amount of slack in the kickdown cable at idle? If the cable is not adjusted correctly, it will think the gas pedal is to the floor and stay in 1st gear, possibly burning up the tranny. The sensor Jamesw is talking about is on the intake by the carb, and is a temp sensor to tell the tranny it is ok to go into o/d. It is an emissions thing - you can ground the wire to the intake and the o/d will function anytime it is at the proper speed.